#include<iostream>

#include<cstring>

#include<cstdlib>

#include<cstdio>

#include<algorithm>

#define ll long long

using namespace std;

const int maxn=;

const ll inf=1e15;

struct poi{int pos, w;}a[maxn];

int n, m, tot, xor0, xor1;

ll sum0, sum1, ans, ans0;

inline void read(int &k)

{

    int f=; k=; char c=getchar();

    while(c<'' || c>'') c=='-' && (f=-), c=getchar();

    while(c<='' && c>='') k=k*+c-'', c=getchar();

    k*=f;

}

inline bool cmp(poi a, poi b){return a.pos<b.pos;}

int main()

{

    read(n); read(m);

    for(int i=;i<=m;i++) read(a[i].pos), read(a[i].w);

    sort(a+, a++m, cmp); m++;

    for(int j=;j<;j++)

    {

        tot=xor0=sum0=xor1=ans0=;

        sum1=(a[].pos==)?inf:;

        for(int i=;i<=m;i++)

        {

            if(a[i].pos-!=a[i-].pos)

            {

                ans0=min(ans0+sum0, ans0+sum1+);

                xor0=sum0=sum1=; xor1=;

            }

            xor0^=(a[i].w&(<<j))!=; xor1^=(a[i].w&(<<j))!=;

            sum0+=xor0; sum1+=xor1;

        }

        ans+=ans0<<j;

    }

    printf("%lld\n", ans);

}